Rework cache key generation a bit.

Cache keys are now based on the previous commands, rather than the previous state
of the filesystem.

pkg/executor/build.go

@@ -18,13 +18,14 @@ package executor
 
 import (
 	"bytes"
-	"encoding/json"
+	"crypto/sha256"
 	"fmt"
 	"io"
 	"io/ioutil"
 	"os"
 	"path/filepath"
 	"strconv"
+	"strings"
 	"time"
 
 	"github.com/google/go-containerregistry/pkg/name"
@@ -85,23 +86,6 @@ func newStageBuilder(opts *config.KanikoOptions, stage config.KanikoStage) (*sta
 	}, nil
 }
 
-// key will return a string representation of the build at the cmd
-func (s *stageBuilder) key(cmd string) (string, error) {
-	fsKey, err := s.snapshotter.Key()
-	if err != nil {
-		return "", err
-	}
-	c := bytes.NewBuffer([]byte{})
-	enc := json.NewEncoder(c)
-	enc.Encode(s.cf)
-	cf, err := util.SHA256(c)
-	if err != nil {
-		return "", err
-	}
-	logrus.Debugf("%s\n%s\n%s\n%s\n", s.baseImageDigest, fsKey, cf, cmd)
-	return util.SHA256(bytes.NewReader([]byte(s.baseImageDigest + fsKey + cf + cmd)))
-}
-
 // extractCachedLayer will extract the cached layer and append it to the config file
 func (s *stageBuilder) extractCachedLayer(layer v1.Image, createdBy string) error {
 	logrus.Infof("Found cached layer, extracting to filesystem")
@@ -129,6 +113,27 @@ func (s *stageBuilder) extractCachedLayer(layer v1.Image, createdBy string) erro
 	return err
 }
 
+func cacheKey(chainID string) (string, error) {
+	return util.SHA256(strings.NewReader(chainID))
+}
+
+func hashDir(dir string) (string, error) {
+	sha := sha256.New()
+	if err := filepath.Walk(dir, func(path string, fi os.FileInfo, err error) error {
+		fileHash, err := util.CacheHasher()(path)
+		if err != nil {
+			return err
+		}
+		if _, err := sha.Write([]byte(fileHash)); err != nil {
+			return err
+		}
+		return nil
+	}); err != nil {
+		return "", err
+	}
+	return string(sha.Sum(nil)), nil
+}
+
 func (s *stageBuilder) build(opts *config.KanikoOptions) error {
 	// Unpack file system to root
 	if _, err := util.GetFSFromImage(constants.RootDir, s.image); err != nil {
@@ -138,7 +143,16 @@ func (s *stageBuilder) build(opts *config.KanikoOptions) error {
 	if err := s.snapshotter.Init(); err != nil {
 		return err
 	}
+
 	args := dockerfile.NewBuildArgs(opts.BuildArgs)
+
+	// Set the initial chainId to be the base image digest, the build args and the SrcContext.
+	srcContextHash, err := hashDir(opts.SrcContext)
+	if err != nil {
+		return err
+	}
+	chainID := s.baseImageDigest + "-" + strings.Join([]string(opts.BuildArgs), ",") + "-" + srcContextHash
+
 	for index, cmd := range s.stage.Commands {
 		finalCmd := index == len(s.stage.Commands)-1
 		command, err := commands.GetCommand(cmd, opts.SrcContext)
@@ -148,13 +162,16 @@ func (s *stageBuilder) build(opts *config.KanikoOptions) error {
 		if command == nil {
 			continue
 		}
+
+		// Add the next command to the cache key.
+		chainID += "-" + command.String()
 		logrus.Info(command.String())
-		cacheKey, err := s.key(command.String())
+		ck, err := cacheKey(chainID)
 		if err != nil {
 			return errors.Wrap(err, "getting key")
 		}
 		if command.CacheCommand() && opts.Cache {
-			image, err := cache.RetrieveLayer(opts, cacheKey)
+			image, err := cache.RetrieveLayer(opts, ck)
 			if err == nil {
 				if err := s.extractCachedLayer(image, command.String()); err != nil {
 					return errors.Wrap(err, "extracting cached layer")
@@ -213,7 +230,7 @@ func (s *stageBuilder) build(opts *config.KanikoOptions) error {
 		}
 		// Push layer to cache now along with new config file
 		if command.CacheCommand() && opts.Cache {
-			if err := pushLayerToCache(opts, cacheKey, layer, command.String()); err != nil {
+			if err := pushLayerToCache(opts, ck, layer, command.String()); err != nil {
 				return err
 			}
 		}